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<h2 id="replaceregexp">ReplaceRegExp</h2>
<h3>Description</h3>
<p><code>ReplaceRegExp</code> is a directory based task for replacing the occurrence of a given
regular expression with a substitution pattern in a selected file or set of files.</p>

<p>The output file is only written if it differs from the existing file.  This prevents spurious
rebuilds based on unchanged files which have been regenerated by this task.</p>

<p>Similar to <a href="../Types/mapper.html#regexp-mapper">regexp type mappers</a> this task needs a
supporting regular expression library and an implementation
of <code class="code">org.apache.tools.ant.util.regexp.Regexp</code>.  See details in the
documentation of the <a href="../Types/regexp.html#implementation">Regexp Type</a>.</p>

<h3>Parameters</h3>
<table class="attr">
  <tr>
    <th scope="col">Attribute</th>
    <th scope="col">Description</th>
    <th scope="col">Required</th>
  </tr>
  <tr>
    <td>file</td>
    <td>file for which the regular expression should be replaced.</td>
    <td>Yes, unless nested <code>&lt;fileset&gt;</code> is used</td>
  </tr>
  <tr>
    <td>match</td>
    <td>The regular expression pattern to match in the file(s)</td>
    <td>Yes, unless nested <code>&lt;regexp&gt;</code> is used</td>
  </tr>
  <tr>
    <td>replace</td>
    <td>The substitution pattern to place in the file(s) in place of the regular expression.</td>
    <td>Yes, unless nested <code>&lt;substitution&gt;</code> is used</td>
  </tr>
  <tr>
    <td>flags</td>
    <td>The flags to use when matching the regular expression.  For more information, consult the
      Perl 5 syntax<br/>
      <q>g</q> : Global replacement.  Replace all occurrences found<br/>
      <q>i</q> : Case Insensitive.  Do not consider case in the match<br/>
      <q>m</q> : Multiline.  Treat the string as multiple lines of input, using <q>^</q>
      and <q>$</q> as the start or end of any line, respectively, rather than start or end of
      string.<br/>
      <q>s</q> : Singleline.  Treat the string as a single line of input, using <q>.</q> to match
      any character, including a newline, which normally, it would not match.
    </td>
    <td>No</td>
  </tr>
  <tr>
    <td>byline</td>
    <td>Process the file(s) one line at a time, executing the replacement on one line at a time
      (<q>true|false</q>).  This is useful if you want to only replace the first occurrence of a
      regular expression on each line, which is not easy to do when processing the file as a
      whole.</td>
    <td>No; defaults to <q>false</q></td>
  </tr>
  <tr>
    <td>encoding</td>
    <td>The encoding of the file. <em>since Apache Ant 1.6</em></td>
    <td>No; defaults to default JVM character encoding</td>
  </tr>
  <tr>
    <td>preserveLastModified</td>
    <td>Keep the file timestamp(s) even if the file(s) is(are) modified.  <em>since Ant
      1.8.0</em>.</td>
    <td>No; defaults to <q>false</q></td>
  </tr>
</table>
<h3>Examples</h3>
<pre>
&lt;replaceregexp file=&quot;${src}/build.properties&quot;
               match=&quot;OldProperty=(.*)&quot;
               replace=&quot;NewProperty=\1&quot;
               byline=&quot;true&quot;/&gt;</pre>
<p>replaces occurrences of the property name <q>OldProperty</q> with <q>NewProperty</q> in a
properties file, preserving the existing value, in the file <samp>${src}/build.properties</samp></p>

<h3>Parameters specified as nested elements</h3>
<p>This task supports a nested <a href="../Types/fileset.html">FileSet</a> element.</p>
<p><em>Since Ant 1.8.0</em>, this task supports any filesystem
based <a href="../Types/resources.html#collection">resource collections</a> as nested elements.</p>
<p>This task supports a nested <a href="../Types/regexp.html">Regexp</a> element to specify the
regular expression.  You can use this element to refer to a previously defined regular expression
datatype instance.</p>

<pre>
&lt;regexp id="id" pattern="alpha(.+)beta"/&gt;
&lt;regexp refid="id"/&gt;</pre>

<p>This task supports a nested <code>substitution</code> element to specify the substitution
pattern.  You can use this element to refer to a previously defined substitution pattern datatype
instance.</p>

<pre>
&lt;substitution id="id" expression="beta\1alpha"/&gt;<br/>
&lt;substitution refid="id"/&gt;</pre>

<h3>Examples</h3>

<p>Replace occurrences of the property name <q>OldProperty</q> with <q>NewProperty</q> in a
properties file, preserving the existing value, in all files ending in <samp>.properties</samp> in
the current directory:</p>
<pre>
&lt;replaceregexp byline=&quot;true&quot;&gt;
    &lt;regexp pattern=&quot;OldProperty=(.*)&quot;/&gt;
    &lt;substitution expression=&quot;NewProperty=\1&quot;/&gt;
    &lt;fileset dir=&quot;.&quot;&gt;
        &lt;include name=&quot;*.properties&quot;/&gt;
    &lt;/fileset&gt;
&lt;/replaceregexp&gt;</pre>

<p>Replace all whitespaces (blanks, tabs, etc) by one blank remaining the line separator:</p>
<pre>
&lt;replaceregexp match="\s+" replace=" " flags="g" byline="true"&gt;
    &lt;fileset dir="${html.dir}" includes="**/*.html"/&gt;
&lt;/replaceregexp&gt;</pre>
<p>Then, input</p>
<pre>
&lt;html&gt;    &lt;body&gt;
&lt;&lt;TAB&gt;&gt;&lt;h1&gt;    T E S T   &lt;/h1&gt;  &lt;&lt;TAB&gt;&gt;
&lt;&lt;TAB&gt;&gt; &lt;/body&gt;&lt;/html&gt;</pre>
<p>is converted to</p>
<pre>
&lt;html&gt; &lt;body&gt;
 &lt;h1&gt; T E S T &lt;/h1&gt; &lt;/body&gt;&lt;/html&gt;</pre>

<p>The task</p>
<pre>
&lt;replaceregexp match="\\n" replace="${line.separator}" flags="g" byline="true"&gt;
    &lt;fileset dir="${dir}"/&gt;
&lt;/replaceregexp&gt;</pre>
<p>replaces all <q>\n</q> markers (beware the quoting of the backslash) by a line break. Then,
input</p>
<pre>one\ntwo\nthree</pre>
<p>is converted to</p>
<pre>
one
two
three</pre>

<p>Beware that inserting line breaks could break file syntax. For example in XML:</p>
<pre>
&lt;root&gt;
    &lt;text&gt;line breaks \n should work in text&lt;/text&gt;
    &lt;attribute value=&quot;but breaks \n attributes&quot;/&gt;
&lt;/root&gt;</pre>

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